Alright guys I know this technical question is posted in odds and ends but since it is not Mack related I posted it here. As you guys know I bought a 1993 Dodge with a Cummins in it and it got great mileage the first tank of fuel (21.55mpg). Mind you my dad filled it up before he brought it to me from 180 miles away and I ran it and filled it and got the above stated mileage. I filled it and used it the same as I did (driving wise) on the first tank but I only got around 17.5mpg. I then filled it and took a highway trip 192miles round trip to get groceries and only got 16.8mpg. Today I drove 120miles round trip to get parts and doing some rough math I am getting about 15 or less now. I havent had any hard head winds when traveling to speak of, it's pretty damn flat on all of my road trips so I have no clue why my fuel mileage since Easter weekend when I bought the rig 'til now has gone to hell. I went to the local mechanic and he was such an arrogant little prick today I was ready to kick his a$$hole right thru his teeth. You can get away with crap like that when you are the only mechanic within 60 mile radius. I wanted to make an appointment for him to trouble shoot it if he thought that was necessary. So he asked me a few questions first about the pickup and I answered the best to my knowledge and his attitude seemed like he could give a shit less about helping me. So I asked to make an appointment and he said for what which I replied to figure out what's wrong. He then began to arrogantly tell me that low power and bad mpg are the two most difficult things to diagnose. Ok I can buy that since there are a lot of variables. So I asked him if changing the air and fuel filter would be a likely place to start since it seems like a simple likely place to start. Then the little bastard begins on a rant about how its a needle in a hay stack and on and on about how difficult it will be to figure this out. I calmly told him I have a hard time believing that this would be a major mechanical failure like he said it could've been (I am not ruling that out but it is on my less likely list of troubleshooting) since there never seemed to be a sudden change in noise, power, smoking or lack there of. He then told me that injectors will go out just like flipping a switch which seems unlikely to me but hey I am no mechanic. So I then asked if I should just throw my engine away since there is no way to trouble shoot or fix it? He told me I dunno maybe. I was so livid I wanted to stomp a mudhole in his ass and walk it dry. Little bastard is lucky that he is so far away from any competition because I bet his attitude would change or he would go out of business. This hasnt been my first run in with him being prick, usually I can just shrug it off but eventually a kicked dog bites back. So after my rant I wanted to aske some of you guys on here what you think as far as trouble shooting. Would a fuel and air filter be a good place to start? I thought after that maybe checking to see if all of the air flow from the turbo to the intake was tight with no leaks. Could the fuel quality be that different from where my dad filled it compared to the two different towns I filled in to make a difference? After that I have no clue. Thanks in advance. HeavyGunner P.S. I started using Lucas fuel additive on the 3rd tank of fuel.